US3979702A - Apparatus and method for oversampled transducers in acoustic surface wave devices - Google Patents
Apparatus and method for oversampled transducers in acoustic surface wave devices Download PDFInfo
- Publication number
- US3979702A US3979702A US05/458,940 US45894074A US3979702A US 3979702 A US3979702 A US 3979702A US 45894074 A US45894074 A US 45894074A US 3979702 A US3979702 A US 3979702A
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- transducer
- acoustic
- frequency
- electro
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/64—Filters using surface acoustic waves
- H03H9/6423—Means for obtaining a particular transfer characteristic
Definitions
- This invention relates generally to acoustic surface wave devices and more particularly to apparatus for improving the frequency characteristics of acoustic surface wave devices.
- acoustic surface wave devices surface waves are propagated between electro-acoustic transducers.
- the transducer configurations determine the transfer characteristics of the surface wave device.
- a surface wave device can be arranged to act as a filter.
- the frequency response characteristics are typically specified.
- f c is the center frequency of the desired frequency response of the acoustic surface wave transducer
- the local maxima or the local minima are typically separated by approximately 1/f c in the time domain.
- electrodes are typically spaced in time (i.e. corresponding to surface wave traversal) 1/2f c apart at positions corresponding to the local maxima and minima.
- the highest frequency which can be accurately transmitted or received by such a sampling density is f c .
- any attempt to provide improved frequency response must involve both the electrode set generating the acoustic surface waves and the electrode set detecting the presence of acoustic surface waves.
- the accuracy of the acoustic surface wave device frequency response is determined by the least accurate response of the two electrode sets.
- the aforementioned and other objects of the present invention are accomplished by providing electro-acoustic transducers with an electrode density above the sampling density determined by the design center frequency.
- the configuration of the electrodes in the increased or over-sampled electrode density transducer is determined by the envelope of time domain representation of the desired frequency response, but the electrodes will not in general fall at positions of local maxima and minima of the time domain representation of the desired frequency response.
- an input electro-acoustic transducer is typically not amplitude-encoded.
- An over-sampled input transducer wherein all electrodes are substantially the same length provides the best directionality for the generated waves.
- Different sampling densities are employed for the input and the output transducers of the acoustic surface wave devices to minimize transfer of undesired frequency components resulting from utilization of oversampled transducer densities.
- FIG. 1 shows a schematic representation of the transformation between the frequency domain and the time domain.
- FIG. 2 shows the method of determining the configuration for overlap amplitude-encoded interleaved electrodes in prior art devices.
- FIG. 3 shows an electroacoustic device having oversampled transducers according to the preferred embodiment of the present invention.
- FIG. 1 a schematic illustration of the transformation between response characteristics in the Frequency Domain 10 and response characteristics in the Time Domain 20 is shown.
- response characteristics are specified in the Frequency Domain, for example, when the optimum response of a filter is selected.
- f c denotes the center frequency
- f h denotes the highest specified frequency.
- the response of an electro-acoustic filter with interleaved electrodes can be more conveniently described between a respresentation in the Frequency Domain and a representation in the Time Domain (e.g. by means of the Fourier analysis) are known to persons skilled in the art.
- the Time Domain function can be transferred to a transducer associated with an Acoustic Wave Propagating Medium 25 by recognizing that the time axis, when multiplied by the velocity of wave propagation in Medium 25, v o , becomes a distance axis for determining relative positions between transducers.
- One set of Electrodes 31 is located at the positions determined by the local minima of the Time Domain function while a second set of Electrodes 41 is located at positions determined by the local maxima of the Time Domain functions.
- Electrodes 31 are coupled to Conductor 30 which can be arbitrarily assigned a negative polarity, while the Electrodes 41 are coupled to Conductor 40 which can arbitrarily be assigned a positive polarity.
- the amplitude of the overlap between the interleaved Electrodes 31 and Electrodes 41 is determined by the relative heights of the local extrema of the Time Domain representation. This determination is illustrated by the Time Domain function indicated by the dotted line.
- the amplitude of the overlap of two interleaved electrodes results in the proportionate amplitude for a generated acoustic wave, or a signal resulting from the detection of an acoustic surface wave, by the two electrodes.
- a first transducer is comprised of Electrodes 51 coupled to Conductor 50 and Electrodes 61 coupled to Conductor 60.
- the first transducer is typically employed as an input transducer.
- the dotted Curve 26 indicates the center frequency of acoustic waves to be propagated from the first transducer to the second transducer.
- the seperation between adjacent Electrodes is substantially constant and is equivalent to a phase of 90° for the center frequency.
- the overlap amplitude transducer electrodes is substantially constant to minimize a spreading of the generated acoustic waves.
- the second transducer is positioned on Medium 25 to intercept acoustic waves launched from an input transducer.
- the second transducer includes Electrodes 32 coupled to Conductor 30 and Electrodes 42 coupled to Conductor 40.
- the Time Domain function which represents the desired device response, is shown superimposed on the second transducer as dotted Curve 27.
- the amplitudes of the Electrodes are determined by the envelope of the curve.
- Adjacent Electrodes are not, in general, coupled to different Conductors.
- the Electrodes are not, in general, positioned at the extrema as indicated by the Time Domain function 27.
- the Electrodes are generally placed on equal distance apart. The maximum distance between adjacent Electrodes can determine a limit to the frequency response of the transducers.
- the first (or input) transducer electrode sampling density is chosen so that there is a higher sampling density than can be employed without compromising the directionality of the generated acoustic waves. It is known to those skilled in the art that for uniformly spaced receiver electrodes, distortion of frequency characteristics above roughly one-half the sampling frequency rate are introduced. However, by choosing the electrode positions symmetrically along the envelope determined by the Time Domain function, the Electrodes (i.e. 51 and 61 of FIG. 3) have substantially the same length. This uniformity of length results in greater directionality for the generated acoustic wave.
- the sampling density of this electrode configuration is 4f c . Error components will be generated by this configuration, but the error components will not be received by a properly selected over-sampled second (or output) transducer.
- the second transducer also has oversampled electrode density. Because of the higher sampling frequency, the detection of all the desired frequencies to f h (c.f. the Frequency Domain function of FIG. 1) can be achieved. Acoustic wave error components generated by the input transducer with a sampling density of 4f c will typically be at frequency in the region of 2f c , which is normally greater than f h . Thus, in the preferred embodiment, frequency up to and including f h can be more accurately detected, while the error component, introduced by the input transducer, will not be detected.
- electrode densities above 2f c / 0.7 provide the best results for the transducer detecting the acoustical surface waves; however, other sampling electrode densities can offer improvement as will be clear to those skilled in the art. It is found that electrode densities above 4f c , which can result in three electrodes being associated with a local maxima or minima in a Time Domain representation, introduces distortion in the fidelity of signal detection. Therefore, the electrode sampling density of 4f c of the input transducer provides an upper limit to the electrode sampling density.
- the design center frequency of the input transducer need not be identical with the design center frequency of the output transducer. Nonetheless, the density of the output transducer electrodes is limited by the sampling electrode density of the input transducer.
- the electrode spacing need not be uniform as is shown in FIG. 3. However, it will be apparent that deviations from a uniform electrode density cause distortions which are a function of the largest interelectrode transducer spacing.
Abstract
Description
Claims (10)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US05/458,940 US3979702A (en) | 1974-04-08 | 1974-04-08 | Apparatus and method for oversampled transducers in acoustic surface wave devices |
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US05/458,940 US3979702A (en) | 1974-04-08 | 1974-04-08 | Apparatus and method for oversampled transducers in acoustic surface wave devices |
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US3979702A true US3979702A (en) | 1976-09-07 |
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US05/458,940 Expired - Lifetime US3979702A (en) | 1974-04-08 | 1974-04-08 | Apparatus and method for oversampled transducers in acoustic surface wave devices |
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Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4126838A (en) * | 1977-09-26 | 1978-11-21 | Rca Corporation | Uniform surface acoustic wave transducer configuration having improved frequency selectivity |
US4184052A (en) * | 1978-01-16 | 1980-01-15 | Texas Instruments Incorporated | AM/FM time division surface wave device transmitter |
DE3038056A1 (en) * | 1979-10-08 | 1981-04-16 | Toko, Inc., Tokyo | ACOUSTIC SURFACE WAVE DEVICE |
US5073763A (en) * | 1990-11-02 | 1991-12-17 | R.F. Monolithics, Inc. | Group single-phase unidirectional transducers with 3/8λand 5/8λ sampling |
US5396200A (en) * | 1990-06-13 | 1995-03-07 | Siemens Aktiengesellschaft | Interdigital transducer with finger-width weighting for surface wave arrangements |
US5521565A (en) * | 1988-09-28 | 1996-05-28 | Siemens Aktiengesellschaft | Surface wave interdigital transducer and surface wave filter with symmetric or predeterminable asymmetric transfer characteristic between input and output |
US5838091A (en) * | 1995-04-04 | 1998-11-17 | Murata Manufacturing Co., Ltd. | Surface acoustic wave device including IDT electrode having solid electrode portion and split electrode portion |
US6005326A (en) * | 1996-10-14 | 1999-12-21 | Nec Corporation | Surface acoustic wave device |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3663899A (en) * | 1969-04-16 | 1972-05-16 | Thomson Csf | Surface-wave electro-acoustic filter |
US3755761A (en) * | 1971-12-30 | 1973-08-28 | Texas Instruments Inc | Surface wave transversal frequency filter |
US3803520A (en) * | 1973-04-26 | 1974-04-09 | Hughes Aircraft Co | Acoustic surface wave device with improved transducer |
US3825860A (en) * | 1972-12-13 | 1974-07-23 | Us Air Force | Surface wave delay line with quarter-wave taps |
US3845419A (en) * | 1973-04-02 | 1974-10-29 | G Nudd | Acoustic surface wave device |
US3855556A (en) * | 1973-04-02 | 1974-12-17 | Texas Instruments Inc | Selectable frequency bandpass filter |
-
1974
- 1974-04-08 US US05/458,940 patent/US3979702A/en not_active Expired - Lifetime
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3663899A (en) * | 1969-04-16 | 1972-05-16 | Thomson Csf | Surface-wave electro-acoustic filter |
US3755761A (en) * | 1971-12-30 | 1973-08-28 | Texas Instruments Inc | Surface wave transversal frequency filter |
US3825860A (en) * | 1972-12-13 | 1974-07-23 | Us Air Force | Surface wave delay line with quarter-wave taps |
US3845419A (en) * | 1973-04-02 | 1974-10-29 | G Nudd | Acoustic surface wave device |
US3855556A (en) * | 1973-04-02 | 1974-12-17 | Texas Instruments Inc | Selectable frequency bandpass filter |
US3803520A (en) * | 1973-04-26 | 1974-04-09 | Hughes Aircraft Co | Acoustic surface wave device with improved transducer |
Cited By (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4126838A (en) * | 1977-09-26 | 1978-11-21 | Rca Corporation | Uniform surface acoustic wave transducer configuration having improved frequency selectivity |
US4184052A (en) * | 1978-01-16 | 1980-01-15 | Texas Instruments Incorporated | AM/FM time division surface wave device transmitter |
DE3038056A1 (en) * | 1979-10-08 | 1981-04-16 | Toko, Inc., Tokyo | ACOUSTIC SURFACE WAVE DEVICE |
US4330767A (en) * | 1979-10-08 | 1982-05-18 | Toko, Inc. | Surface acoustic wave device |
US5521565A (en) * | 1988-09-28 | 1996-05-28 | Siemens Aktiengesellschaft | Surface wave interdigital transducer and surface wave filter with symmetric or predeterminable asymmetric transfer characteristic between input and output |
US5396200A (en) * | 1990-06-13 | 1995-03-07 | Siemens Aktiengesellschaft | Interdigital transducer with finger-width weighting for surface wave arrangements |
US5073763A (en) * | 1990-11-02 | 1991-12-17 | R.F. Monolithics, Inc. | Group single-phase unidirectional transducers with 3/8λand 5/8λ sampling |
US5838091A (en) * | 1995-04-04 | 1998-11-17 | Murata Manufacturing Co., Ltd. | Surface acoustic wave device including IDT electrode having solid electrode portion and split electrode portion |
US6005326A (en) * | 1996-10-14 | 1999-12-21 | Nec Corporation | Surface acoustic wave device |
US6040651A (en) * | 1996-10-14 | 2000-03-21 | Nec Corporation | Surface acoustic wave device |
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Legal Events
Date | Code | Title | Description |
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AS | Assignment |
Owner name: MAGNAVOX ELECTRONIC SYSTEMS COMPANY Free format text: CHANGE OF NAME;ASSIGNOR:MAGNAVOX GOVERNMENT AND INDUSTRIAL ELECTRONICS COMPANY A CORP. OF DELAWARE;REEL/FRAME:005900/0278 Effective date: 19910916 |
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AS | Assignment |
Owner name: CITICORP USA, INC., NEW YORK Free format text: SECURITY INTEREST;ASSIGNOR:MESC ELECTRONIC SYSTEMS, INC.;REEL/FRAME:006818/0404 Effective date: 19931022 |
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AS | Assignment |
Owner name: MAGNAVOX ELECTRONIC SYSTEMS COMPANY, INDIANA Free format text: CHANGE OF NAME;ASSIGNOR:CITICORP USA, INC.;REEL/FRAME:007927/0147 Effective date: 19941219 Owner name: MESC ELECTRONIC SYSTEMS, INC., INDIANA Free format text: RELEASE OF SECURITY INTEREST;ASSIGNOR:CITICORP USA, INC.;REEL/FRAME:008098/0523 Effective date: 19940831 Owner name: MAGNAVOX ELECTRONIC SYSTEMS COMPANY, INDIANA Free format text: RELEASE BY SECURED PARTY;ASSIGNOR:CITICORP USA, INC.;REEL/FRAME:007927/0104 Effective date: 19951214 |